Thermal managing end plate for fuel cell stack assembly

ABSTRACT

Fuel cell stack assemblies ( 100 ) have a positive end plate ( 200 ) and a negative end plate ( 300 ), The end plates ( 200, 300 ) can be formed from a central structural element ( 220, 320 ) with an insulating end plate cover ( 210, 310 ) and an insulating end plate manifold ( 230, 330 ). A plurality of cathode plates ( 150 ) and a plurality of fuel cell assemblies ( 250 ) can be arranged in a stack having an alternating pattern of cathode plates ( 150 ) and fuel cell assemblies ( 250 ), with the positive end plate ( 200 ) and the negative end plate ( 300 ) provided on either end of the stack of cathode plates and fuel cell assemblies.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a 371 US National Stage of InternationalPatent Application No. PCT/GB2019/051073 filed Apr. 16, 2019, whichclaims priority of GB Patent Application No. 1806344.6 filed on Apr. 18,2018, the entire contents of which are hereby incorporated by referenceas if fully set forth herein.

FIELD OF THE DISCLOSURE

This disclosure is in the field of endplates for fuel cell stackassemblies. In particular, the disclosure relates to devices and methodsfor use in providing thermal insulation to fuel cell stack assemblies.

BACKGROUND

Conventional electrochemical fuel cells convert fuel and oxidant intoelectrical energy and a reaction product. A typical fuel cell comprisesa plurality of layers, including an ion transfer membrane sandwichedbetween an anode and a cathode to form a membrane-electrode assembly, orMEA.

Sandwiching the membrane and electrode layers is an anode fluid flowfield plate for conveying fluid fuel to the anode, and a cathode fluidflow field plate for conveying oxidant to the cathode and for removingreaction by-products. Fluid flow field plates are conventionallyfabricated with fluid flow passages formed in a surface of the plate,such as grooves or channels in the surface presented to the porouselectrodes.

A typical single cell of a proton exchange membrane fuel cell will,under normal operating conditions, provide an output voltage between 0.5and 1.0 Volt. Many applications and electrical devices require highvoltages for efficient operation. These elevated voltages areconventionally obtained by connecting a plurality of individual cells inseries to form a fuel cell stack. To decrease the overall volume andweight of the stack, a bipolar plate arrangement is utilised to providethe anode fluid flow field plate for one cell, and the cathode fluidflow field plate for the adjacent cell. Suitable flow fields areprovided on each side of the plate, carrying fuel (eg. hydrogen, or ahydrogen rich gas) on one side and oxidant (eg. air) on the other side.Bipolar plates are both gas impermeable and electrically conductive andthereby ensure efficient separation of reactant gases whilst providingan electrically conducting interconnect between cells. Fluids areconventionally delivered to each fluid flow field plate by way of commonmanifolds that run down the height of the stack, formed from alignedapertures in each successive plate. The area of a single fuel cell canvary from a few square centimetres to hundreds of square centimetres. Astack can consist of a few cells to hundreds of cells connected inseries using bipolar plates. Two current collector plates, one at eachend of the complete stack of fuel cells, are used to provide connectionto the external circuit.

There are a number of important considerations in assembling the fuelcell stack. Firstly, the individual layers or plates must be positionedcorrectly to ensure that gas flow channels and manifolds are in correctalignment. Secondly, the contact pressure between adjacent plates isused to form gas tight seals between the various elements in themanifolds and gas flow channels. Conventionally, the gas tight sealsinclude compressible gaskets that are situated on the surfaces ofpredetermined faces of the plates. Therefore, in order to ensure propergas tight sealing, an appropriate compression force must be applied toall of the plates in the stack, orthogonal to the surface planes of theplates in the stack, to ensure that all gaskets and sealing surfaces areproperly compressed. Thirdly, a compressive force is essential to ensuregood electrical connectivity between adjacent layers. At the outer endsof the stack, substantially rigid end plates are usually deployed forthe application of suitable compression forces to retain the stack inits assembled state.

For optimum performance of a fuel cell stack, compression of the MEAacross each fuel cell must be sufficiently high to avoid higher contactresistance and lower efficiency due to ohmic losses. It is alsodesirable to provide even compression of each MEA across the surface ofeach fuel cell in order to avoid the formation of shear stress exertedon the MEA, which can lead to cell failure due to pin-holing of the MEA.Uniformity of compression throughout a fuel cell stack is important tostack electrical performance, which is limited by electrical variationsthroughout the stack, which can have tens or hundreds of fuel cellscontained in a stack under several tons of compressive force between apair of end plates. It is important to avoid any variations from beingintroduced during the manufacturing and assembly processes or fromuneven component thicknesses, either laterally across the width of eachplate or longitudinally along the length of each flow channel of eachplate, as these variations can lead to problems with uniformitythroughout a fuel cell stack having tens or hundreds of repeatedcomponent layers.

Further, for optimum performance of a fuel cell stack, temperaturevariations between the fuel cells within the stack must be minimized,and compatibility with a wide range of temperatures for operationalenvironments and climates are necessary for commercial applications

Thus, there is a need for improved end plates for fuel cell stacks thatcan provide the necessary functionalities for commercial applications.The disclosure is directed to these and other important needs.

DISCLOSURE

The present disclosure provides aspects of end plates for fuel cellstack assemblies, the end plates comprising a central structural elementhaving a top face and a bottom face, an end plate cover covering the topface, and an end plate manifold covering the bottom face. The end platescan have a central structural element formed from aluminum. The endplates can have a central structural element formed from a para-aramidsynthetic fiber or a carbon fiber composite. The end plates can have aend plate cover, end plate manifold, or both formed from an electricallyinsulating material. The electrically insulating material is PC-ABSblends, PET, glass-filled PET, PA6, glass-filled PA6, PBT, PEI, ormixtures thereof. The end plate cover and end plate manifold can bereleasably engageable to each other through a portion of the centralstructural element via a plurality of snap clips. The central structuralelement can be formed with a rib-and-core or honeycombed structure withvoids formed extending from the top face to the bottom face. The endplate manifold can be provided with a ribbed structure to provide forair flow channels from a first side edge to an opposing side edge. Insome implementations, the end plates can be positive end plates havingpositive end plate manifolds having air flow channels formed as straightairflow channels. In other implementations, the end plates can benegative end plates having negative end plate manifolds having air flowchannels formed as sinusoidal-wave-shaped airflow channels.

The present disclosure provides aspects of fuel cell stack assembliescomprising a positive end plate as described herein, a negative endplate as described herein, a plurality of cathode plates and a pluralityof fuel cell assemblies, arranged in a stack having an alternatingpattern of cathode plates and fuel cell assemblies. The positive endplate and the negative end plate can be provided on either end of thestack of cathode plates and fuel cell assemblies. The final cathodeplate in the stack can be adjacent to the positive end plate. Thenegative end plate can be adjacent to the first fuel cell assembly. Thefuel cell stack assembly can be under compressive force between thepositive end plate and the negative plate. The fuel cell stack assemblycan have a positive end plate and a negative end plate provided withairflow channels. The airflow channels of the positive end plate can beformed as airflow channels having straight-walls from the first sideedge to the opposing side edge, and the airflow channels of the negativeend plate can be formed as sinusoidal-wave-shaped airflow channels fromthe first side edge to the opposing side edge. Current collection can beachieved directly from each end cell or via a current collector platethat is disposed between each end cells and adjacent end plate.

The general description and the following detailed description areexemplary and explanatory only and are not restrictive of thedisclosure, as defined in the appended claims. Other aspects of thepresent disclosure will be apparent to those skilled in the art in viewof the detailed description of the disclosure as provided herein.

DRAWINGS

The summary, as well as the following detailed description, is furtherunderstood when read in conjunction with the appended drawings. For thepurpose of illustrating the disclosure, there are shown in the drawingsexemplary implementations of the disclosure; however, the disclosure isnot limited to the specific methods, compositions, and devicesdisclosed. In the figures, like reference numerals designatecorresponding parts throughout the different views. All callouts andannotations are hereby incorporated by this reference as if fully setforth herein. In addition, the drawings are not necessarily drawn toscale. In the drawings:

FIG. 1 illustrates aspects of an exploded side view of components of afuel cell stack assembly of the present disclosure;

FIG. 2 illustrates aspects of an exploded side view of components of apositive end plate of the present disclosure; and

FIG. 3 illustrates aspects of an exploded side view of components of anegative end plate of the present disclosure.

FURTHER DISCLOSURE

The present disclosure may be understood more readily by reference tothe following detailed description taken in connection with theaccompanying figures and examples, which form a part of this disclosure.It is to be understood that this disclosure is not limited to thespecific devices, methods, applications, conditions or parametersdescribed and/or shown herein, and that the terminology used herein isfor the purpose of describing particular exemplars by way of exampleonly and is not intended to be limiting of the claimed disclosure. Also,as used in the specification including the appended claims, the singularforms “a,” “an,” and “the” include the plural, and reference to aparticular numerical value includes at least that particular value,unless the context clearly dictates otherwise. The term “plurality”, asused herein, means more than one. When a range of values is expressed,another exemplar includes from the one particular value and/or to theother particular value. Similarly, when values are expressed asapproximations, by use of the antecedent “about,” it will be understoodthat the particular value forms another exemplar. All ranges areinclusive and combinable.

It is to be appreciated that certain features of the disclosure whichare, for clarity, described herein in the context of separate exemplar,may also be provided in combination in a single exemplaryimplementation. Conversely, various features of the disclosure that are,for brevity, described in the context of a single exemplaryimplementation, may also be provided separately or in anysubcombination. Further, reference to values stated in ranges includeeach and every value within that range.

FIG. 1 shows a schematic side view of an exploded assembly of a fuelcell stack assembly of the present disclosure. A positive end plate 200and a negative end plate 300 are provided on either end of the fuel cellstack assembly 100. When assembled, compressive force is applied betweenthe positive end plate 200 and negative end plate 300 to compress theinternal layers together with sufficient force for optimal electricalperformance. The internal layers include a plurality of cathode plates150 ₁ to 150 _(n) and fuel cell assemblies 250 ₁ to 250 _(n), providedin alternating layers of cathode plates and fuel cell assemblies.Cathode plate 150 _(n) is adjacent to the positive end plate 200, whilethe negative end plate 300 is adjacent to the first fuel cell assembly250 ₁. Current collection can be achieved directly from the end cells,250 ₁ and 250 _(n), or via current collector plates (not shown) that aredisposed between each of the end cells and adjacent end plates 200, 300.The use of current collector plates can avoid ohmic losses and improveperformance.

It has been observed that with conventional end plates, a fuel cellstack assembly cannot be operated in low environmental temperatureswithout cathode air recirculation to maintain an adequate temperature onthe top and bottom fuel cells (the fuel cells within the first and n-thfuel cell assemblies 250 ₁ and 250 _(n)). The temperature problems withthe top and bottom fuel cells were determined to result from overcoolingor overheating due to a lack of thermal insulation provided by the endplates from the surrounding environmental temperatures. Conventional endplates are formed from cast or machined metallic materials which areovermoulded with suitable polymeric compounds to provide suitableelectrical isolation. Alternatively, conventional end plates can beformed as molded polymeric reinforced laminates. Such known endplatescan provide an excess of thermal flux outward from the adjacent fuelcells. In particular, the top fuel cell can experience overcooling, dueto being surrounded on both sides with cathode plates 150 _(n) and 150_(n-1), with only cathode plate 150 _(n-1) experiencing heating fromanother adjacent fuel cell assembly 250 _(n-1). Cathode plate 150 _(n)can provide overcooling as it is not heated by another adjacent fuelcell and is instead thermally contacting the positive end plate 200.Accordingly, the top fuel cell can be overcooled when a conventionalpositive end plate is utilized in a fuel cell stack. Conversely, thebottom fuel cell 250 ₁ can be overheated in certain operationalenvironments as it is only adjacent to one cathode plate and receivessome limited cooling effects from the negative end plate 300.

In one aspect, the present disclosure provides improved designs for thepositive end plates 200 and negative end plates 300 for use in the fuelcell stack assemblies as shown in FIG. 1. It has been discovered throughexperimentation that a more even temperature profile across the fuelcell assemblies 250 ₁ and 250 _(n) can be achieved by utilizing endplates formed from a plurality of components, rather than an overmoldedmetallic piece.

FIG. 2 shows aspects of a schematic of an exploded side view of apositive end plate 200 of the present disclosure. A positive end plate200 can be formed from a central structural element 220, which iscovered on a top face 221 by a positive end plate cover 210, and coveredon a bottom face 222 by a positive end plate manifold 230. Positive endplate manifold 230 is adjacent to the n-th cathode plate 150 _(n) in theassembled fuel cell stack assembly. Central structural element 220 isformed from a sufficiently rigid material in order to provide structuralstrength to withstand the overall compression forces on the assembledfuel cell stack. In certain implementations, the structural element 220can be formed from a lightweight metal such as aluminum. In otherimplementations, rigid materials such as a para-aramid synthetic fiberor carbon fiber composites can be used, provided that strength/weightperformance is adequate to provide desired power/mass density for theoverall fuel cell stack assembly. The positive end plate cover 210 andpositive end plate manifold 230 are formed from electrically insulatingmaterials, such as plastic. In certain implementations, the positive endplate cover 210 and positive end plate manifold 230 are releasablyengageable to each other through a portion of the central structuralelement 220 via a plurality of snap clips. This engagement can aid inthe assembly process, such that the positive end plate 200 can holditself together while the fuel cell stack assembly components arelayered together prior to application of the desired compression force.

In some implementations, positive end plate cover 210 and positive endplate manifold 230 are formed from plastic or polymeric resin materials.Suitable materials can withstand operational temperatures within thefuel cell stack assembly, are compatible with hydrogen gas, and can bePC-ABS blends, PET, glass-filled PET, PA6, glass-filled PA6, PBT, PEI,or mixtures thereof. In certain implementations, one or both of thepositive end plate cover 210 and positive end plate manifold 230 can beformed from glass-filled PET, including RYNITE® sold by DuPont USAPerformance Polymers.

In certain implementations, the thermal insulation is increased byreducing the contact area between the structural element 220 and thepositive end plate cover 210, and reducing the contact area between thestructural element 220 and positive end plate manifold 230. The contactareas can be reduced by removing as much of the bulk material within thestructural element 220 by creating a rib-and-core or honeycombedstructure in the structural element 220, with voids formed extendingfrom the top face 221 to the bottom face 222. The inclusion of voids inthe structural element 220 reduces the thermal flux transfer pathwaysfrom the outside environment of the fuel cell stack assembly and thetop-most fuel cell assembly 250 _(n).

The positive end plate manifold 230 can be provided with a ribbedstructure to provide for fluid flow channels as well as a reducedcontact area between the positive end plate manifold 230 and thestructural element 220. Air flow is provided from one side edge 231 toan opposing side edge 232 of the positive end plate manifold 230. Insome implementations, in order to reduce heat removal and avoidovercooling of the top-most fuel cell assembly 250 _(n) straight-walledairflow channels can be provided to allow for the fastest airflowthrough past the positive end plate manifold 230 and adjacent cathodeplate 150 _(n) and avoid excessive heat removal.

FIG. 3 shows aspects of a schematic of an exploded side view of anegative end plate 300 of the present disclosure. A negative end plate300 can be formed from a central structural element 320, which iscovered on a top face 322 by a negative end plate cover 310, and coveredon a bottom face 321 by a negative end plate manifold 330. Negative endplate manifold 330 is adjacent to the first fuel cell assembly 250 ₁ inthe assembled fuel cell stack assembly. Central structural element 320is formed from a sufficiently rigid material in order to providestructural strength to withstand the overall compression forces on theassembled fuel cell stack. In certain implementations, the structuralelement 320 can be formed from a lightweight metal such as aluminum. Inother implementations, rigid materials such as a para-aramid syntheticfiber or carbon fiber composites can be used, provided thatstrength/weight performance is adequate to provide desired power/massdensity for the overall fuel cell stack assembly. The negative end platecover 310 and negative end plate manifold 330 are formed fromelectrically insulating materials, such as plastic. In certainimplementations, the negative end plate cover 310 and negative end platemanifold 330 are releasably engageable to each other through a portionof the central structural element 320 via a plurality of snap clips.This engagement can aid in the assembly process, such that the negativeend plate 300 can hold itself together while the fuel cell stackassembly components are layered together prior to application of thedesired compression force.

In some implementations, negative end plate cover 310 and negative endplate manifold 330 are formed from plastic or polymeric resin materials.Suitable materials can withstand operational temperatures within thefuel cell stack assembly, are compatible with hydrogen gas, and can bePC-ABS blends, PET, glass-filled PET, PA6, glass-filled PA6, PBT, PEI,or mixtures thereof. In certain implementations, one or both of thenegative end plate cover 310 and negative end plate manifold 330 can beformed from glass-filled PET, including RYNITE® sold by DuPont USAPerformance Polymers.

In certain implementations, the thermal insulation is increased byreducing the contact area between the structural element 320 and thenegative end plate cover 310, and reducing the contact area between thestructural element 320 and negative end plate manifold 330. The contactareas can be reduced by removing as much of the bulk material within thestructural element 320 by creating a rib-and-core or honeycombedstructure in the structural element 320, with voids formed extendingfrom the top face 322 to the bottom face 321. The inclusion of voids inthe structural element 320 reduces the thermal flux transfer pathwaysfrom the outside environment of the fuel cell stack assembly and thefirst fuel cell assembly 250 ₁.

The negative end plate manifold 330 can be provided with a ribbedstructure to provide for fluid flow channels as well as a reducedcontact area between the negative end plate manifold 330 and thestructural element 320. Air flow is provided from one side edge 331 toan opposing side edge 332 of the negative end plate manifold 330. Insome implementations, in order to increase heat removal and avoidoverheating of the first fuel cell assembly 250 ₁,sinusoidal-wave-shaped airflow channels can be provided to slow theairflow through past the negative end plate manifold 330 and adjacentfuel cell assembly 250 ₁ and avoid excessive heat buildup. Furtherdescription of suitable sinusoidal wave-shaped airflow channels isprovided in co-pending UK patent application entitled “COOLING PLATESFOR FUEL CELLS” filed on the same day as this application, the contentsof which are hereby incorporated by reference in their entirety.

In some aspects, the present disclosure provides for an asymmetricalfuel cell stack assembly having a positive end plate and a negative endplate which have different structural features in order to havedifferent thermal transfer properties. As described above, the negativeend plate can utilize a negative end plate manifold having air flowchannels designed for greater heat removal from an adjacent component ascompared to the positive end plate manifold, which has air flow channelsdesigned for less heat removal from an adjacent component. Such animplementation was found to provide the optimal balance of heat removalfrom an operational fuel cell stack assembly and thermal insulation froma surrounding environmental condition. Accordingly, the potentialoperating temperature window can be increased.

EXAMPLE 1

A negative end plate 300 of the present disclosure as depicted in FIG. 3was modeled for 3D FEA thermal analysis. The negative end plate 300, wasmodeled from an aluminum central structural element 320, which iscovered on a top face 322 by a negative end plate cover 310, and coveredon a bottom face 321 by a negative end plate manifold 230. The negativeend plate cover 310 and the negative end plate manifold 230 were modeledas glass-filled PA6 nylon. A conventional end plate, formed from cast,then machined, aluminum overmolded with glass-filled PA6 nylon wasmodeled for 3D FEA thermal analysis for comparison. Heat loss wasreduced from 25.27 W to 17.6 W.

EXAMPLE 2

A positive end plate 200 of the present disclosure as depicted in FIG. 3was modeled for 3D FEA thermal analysis. The positive end plate 200, wasmodeled from an aluminum central structural element 220, which iscovered on a top face 221 by a positive end plate cover 210, and coveredon a bottom face 222 by a positive end plate manifold 230. The positiveend plate cover 210 and the positive end plate manifold 230 were modeledas glass-filled PA6 nylon. A conventional end plate, formed from cast,then machined, aluminum overmolded with glass-filled PA6 nylon wasmodeled for 3D FEA thermal analysis for comparison. Heat loss wasreduced from 28.78 W to 20.85 W.

Those of ordinary skill in the art will appreciate that a variety ofmaterials can be used in the manufacturing of the components in thedevices and systems disclosed herein. Any suitable structure and/ormaterial can be used for the various features described herein, and askilled artisan will be able to select an appropriate structures andmaterials based on various considerations, including the intended use ofthe systems disclosed herein, the intended arena within which they willbe used, and the equipment and/or accessories with which they areintended to be used, among other considerations. Conventional polymeric,metal-polymer composites, ceramics, and metal materials are suitable foruse in the various components. Materials hereinafter discovered and/ordeveloped that are determined to be suitable for use in the features andelements described herein would also be considered acceptable.

When ranges are used herein for physical properties, such as molecularweight, or chemical properties, such as chemical formulae, allcombinations, and subcombinations of ranges for specific exemplartherein are intended to be included.

The disclosures of each patent, patent application, and publicationcited or described in this document are hereby incorporated herein byreference, in its entirety.

Those of ordinary skill in the art will appreciate that numerous changesand modifications can be made to the exemplars of the disclosure andthat such changes and modifications can be made without departing fromthe spirit of the disclosure. It is, therefore, intended that theappended claims cover all such equivalent variations as fall within thetrue scope of the disclosure as defined in the appended claims.

The invention claimed is:
 1. A negative end plate (300) comprising: acentral structural element (320) having a top face (322) and a bottomface (321); a negative end plate cover (310) covering the top face(322); and a negative end plate manifold (330) covering the bottom face(321); wherein: the negative end plate cover (310) and negative endplate manifold (330) are releasably engageable to each other through aportion of the central structural element (320) via a plurality of snapclips.
 2. The negative end plate of claim 1, wherein: the centralstructural element (320) is formed with a rib-and-core or honeycombedstructure with voids formed extending from the top face (321) to thebottom face (322).
 3. The negative end plate of claim 1, wherein: thenegative end plate manifold (330) is provided with a ribbed structure toprovide for air flow channels from a first side edge (331) to anopposing side edge (332).
 4. The negative end plate of claim 3, whereinthe air flow channels are formed as sinusoidal wave-shaped airflowchannels.
 5. A positive end plate (200) comprising: a central structuralelement (220) having a top face (221) and a bottom face (222); apositive end plate cover (210) covering the top face (221); and apositive end plate manifold (230) covering the bottom face (222);wherein: the positive end plate cover (210) and positive end platemanifold (230) are releasably engageable to each other through a portionof the central structural element (220) via a plurality of snap clips.6. The positive end plate (200) of claim 5, wherein: the centralstructural element (220) is formed with a rib-and-core or honeycombedstructure with voids formed extending from the top face (222) to thebottom face (221).
 7. The positive end plate (200) of claim 5, wherein:the positive end plate manifold (230) is provided with a ribbedstructure to provide for air flow channels from a first side edge (231)to an opposing side edge (232).
 8. The positive end plate (200) of claim7, wherein the air flow channels are formed as airflow channels havingstraight-walls from the first side edge (231) to the opposing side edge(232).
 9. A fuel cell stack assembly (100) comprising: a positive endplate (200) further comprising; a central structural element (220)having a top face (221) and a bottom face (222); a positive end platecover (210) covering the top face (221); and a positive end platemanifold (230) covering the bottom face (222); a negative end place(300) further comprising; a central structural element (320) having atop face (322) and a bottom face (321); a negative end plate cover (310)covering the top face (322); and a negative end plate manifold (330)covering the bottom face (321); and a plurality of cathode plates (150 ₁to 150 _(n)) and a plurality of fuel cell assemblies (250 ₁ to 250_(n)), arranged in a stack having an alternating pattern of cathodeplates and fuel cell assemblies; wherein the positive end plate (200)and the negative end plate (300) are provided on either end of the stackof cathode plates and fuel cell assemblies; wherein: the positive endplate (200) and the negative end plate (300) each are provided withairflow channels, the airflow channels of the positive end plate (200)are formed as airflow channels having straight-walls from the first sideedge (231) to the opposing side edge (232), and the airflow channels ofthe negative end plate (300) are formed as sinusoidal-wave shapedairflow channels from the first side edge (331) to the opposing sideedge (332).